The present invention relates to the field of mass storage devices. More particularly, this invention relates to an improved preamp for magnetic recording in a disc drive.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One common place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer head to various locations over the disc, and a write head in the transducer head, and a preamp for providing a write current impulse to drive the write head to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully, retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer head is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the disc. Disc drive systems read and write information stored on tracks on the discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on a surface of the disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the disc. Similarly, reading data on the disc is accomplished by positioning the read/write head above a target track and reading the stored material on the disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of the disc drive. Servo feedback information is used to accurately locate the transducer head. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
The actuator/arm is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft/post is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
Magnetic recording on a disc of a disc drive is a well developed and important technology. Of particular interest is digital, or more precisely binary storage in which the disc is magnetized in one direction for one state and in another direction for another state. A write head attached to the transducer of the disc drive impresses a magnetization on the disc in either one direction or another, dependent on the data signal. The signal thus recorded on the media is subsequently read by a read head using techniques well known in the art.
Generally thin-film heads are used for magnetic recording on the disc because of their small size and their light-weightedness. The problem with thin-film heads is that they are so light-weighted that the head cannot adequately dissipate heat. The current methods of magnetic recording drives the write head continuously during the entire bit or cell period, with the polarity of the drive current determined by the data. That is the duty cycle is nearly 100%. This generally requires auxiliary cooling devices to increase the heat dissipation. This however increases the head weight and further complicates its otherwise light-weight simple structure. Also the continuous write current technique makes it increasingly difficult to write data using a continuous current at higher transfer rates such as greater than one gigabit (Gb) per second (1xc3x97109 bits/sec), due to various factors including stray inductance and capacitance along the conductive paths between the heads and the preamp, the slew rates in the positive and negative transitions, and the power dissipated by the preamp.
What is needed is a write head including a preamp that is smaller, writes faster, requires lower power and minimizes head heating.
An information handling system, such as a disc drive, includes a base, a disc rotatably attached to the base, and an actuator assembly movably attached to the base. Attached to one end of the actuator assembly is a write head having a predetermined head gap. The write head is in transducing relationship with the disc. The write head operatively coupled to a preamp current driver circuit for providing a write current impulse to drive the write head, and a data pulse circuit for supplying digital data signal in the form of data pulses based on an input data pattern. The preamp current driver circuit is operatively coupled to the data pulse circuit. The preamp current driver circuit further includes a pair of voltage driven switches to provide a write current impulse of opposite polarity based on the input data pattern. The preamp current driver circuit further includes a pair of current driven switches to receive the write current impulse from the pair of voltage driven switches, and provide a sequence of write current impulses of opposite polarity to the write head for effecting magnetic recording on the disc of the disc drive based on the input data pattern. The voltage driven switches further change the polarity of the write current impulse anytime near an end of the sequence of write current impulses. This technique does not involve driving the write head continuously during an entire bit or cell time. This technique enables the recording to be done with write current impulses which are generated at edges of the bit or cell time. This is generally possible because the field generated from the write head is generally large enough to magnetize or stamp media beyond a write head gap.
In this embodiment, the preamp current driver circuit generates a leading edge and trailing edge write current transition impulses corresponding to an input data pattern. In general a disc is moving past the write head, and this disc movement tends to extend the amount of the disc being magnetized during a time the write head field existing with sufficient strength to saturate the disc. In this embodiment the leading and trailing edge current transition impulses are of sufficient positive and negative polarity to saturate the disc. In an another embodiment, the preamp current driver circuit generates a sequence of same polarity write current impulses (same as the leading edge transition impulse) having a predetermined repetition period based on the predetermined head gap of the write head, and a velocity of the disc rotating past the write head when a time for the length of recording between the leading and the trailing edge transition impulses are greater than a time for effective recording by the write head gap. The sequence of write current impulses generated by the preamp current driver circuit are sufficient to maintain a substantially equalized recorded continuum between the transition impulses when the time for the length of recording between the leading and the trailing edge transition impulses are greater than a time for effective recording by the write head gap. In one embodiment the leading edge write current transition impulse occurs at the beginning of an input data pattern, and the trailing edge write current transition impulse occurs at the end of the input data pattern. In another embodiment the leading and trailing edge write current transition impulses are of positive and negative polarity and are of sufficient amplitude to saturate the disc respectively.
Advantageously, the improved preamp set forth above, allows the preamp to input lower power, and higher peak currents into the write head. Further the improved preamp eliminates the need for write current overshoot adjustments, and provides faster write current rise times, since the impulses eliminate the need for maintaining steady current to the write head. Further the write current impulses having a higher peak currents enables writing higher coercivity media faster than the current techniques. This improved preamp generating write current impulses results in less heat being generated at the write head, thereby avoiding the overheating problem existing in the current designs. Also this improved method of recording permits faster field raise times, and further simplifies the preamp current drive circuit design. Also the faster raise times improves a transition zone on the disc which can result in improved signal to noise ratio performance.